In the present work, new and advanced methods for the investigation of methanol and hydrogen powered fuel cells were analyzed. Synchrotron radiography and tomography were applied to investigate materials and transport processes in operating fuel cells “in‐situ” and non‐destructively. The corrosion of ruthenium is a key issue during aging of direct methanol fuel cells (DMFC). Therefore the influence of different aging processes on the distribution of ruthenium is of great interesting. An imaging In the present work, new and advanced methods for the investigation of methanol and hydrogen powered fuel cells were analyzed. Synchrotron radiography and tomography were applied to investigate materials and transport processes in operating fuel cells “in‐situ” and non‐destructively. The corrosion of ruthenium is a key issue during aging of direct methanol fuel cells (DMFC). Therefore the influence of different aging processes on the distribution of ruthenium is of great interesting. An imaging method based on X‐ray absorption spectroscopy (XAS) was applied to investigate the changes in the distribution of fuel cell catalysts three‐dimensionally. Using monoenergetic synchrotron radiation it was shown that the distribution of ruthenium (Ru) in the anode catalyst changes after application of an accelerated aging procedure. A strong influence on the flowfield and the gas diffusion layer structures on the Ru distribution were found in the gas diffusion electrode at the anode side. Additionally some ruthenium moves through the membrane from the anode to the cathode. The redistribution caused by the accelerated aging procedure strongly differs from that obtained after aging under realistic stack operation (here over 1700 h) of a fuel cell in a pallet transporter. For the tomographic investigations samples were taken out from a stack operation in aged membrane electrode assembly (MEA) and were analyzed ex‐situ. It was shown that the Ru redistribution can be attributed to mass transport processes (CO2 and H2O) in the gas diffusion layer (GDL). Other high energy resolved measurements showed that the strength of the oxidation of ruthenium and platinum depends on the spatial distribution of the ruthenium. Last mentioned ‐ also for the platinum catalyst ‐ could be given quantitatively by means of this newly developed method. In the second part of this work high temperature polymer electrolyte fuel cells (HT‐PEFC) were investigated. No liquid water can be found due to the high operation temperature of 160‐200°C in this cell type. Hence conventional analysis methods are not applicable here. In especial the product water is very important for the electrical conductivity of the membrane and changes the state of the phosphoric acid inside the membrane and the electrodes. For the first time, the water balance in a HT-PEFC at different operating conditions was characterized in‐situ during cell operation. The characterization was based on measured changes in the membrane transmittance and its thickness. Suitable models allowed calculating the water balance of the membrane. The influence of different operating conditions on the redistribution of the phosphoric acid between the electrodes and in the membrane was analyzed. The analysis is complemented with investigations of polarization curve recording and electrochemical impedance spectroscopy.…